Apprehensive about taking the next step

I am in a super long term committed relationship (6yrs). There were plans to get married after both of us were firmly established in our careers. This person is my ideal match for me in every way except.... physically. In the time we have been dating she has, well... let herself go, to be blunt. She claims that she doesn't have the time to workout or the energy after work despite being home two hours before I am and having approximately 2.5 months of vacation/free time(shes a teacher). Yet I find the time to participate in rec sports and other physically activities while working year round, longer days and sometimes weekends. Because of this I am apprehensive with the idea of marriage because I feel like I'd marry a friend instead of a lover. I feel like I may have a point because we are both in our late 20's and I am under the impression most people marry someone they find attractive both mentally and physically. I have attempted to mention is in the most round about, sugar coated way possible and the message is either, never received or we get into an argument about it. Am I being shallow? Is getting hung up on appearance immature? Is it out of line to expect my partner to be in similar shape as me? We were both college athlete's for goodness sakes!!!!

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